Field of the Invention
The present invention relates to a method for processing a signal provided by a bidirectional sensor as well as to a device for the implementation of such a method.
The field of the present invention is more particularly the field of the management of signals provided by sensors in an engine of a vehicle, for example an automotive vehicle, so as to determine parameters of the engine with a view to managing the proper operation of the latter.
Description of the Related Art
In an internal combustion engine, there is generally at least one movable piston for varying the volume of a combustion chamber. Admission and exhaust of fluids in combustion chambers are usually carried out with the aid of poppet valves controlled by at least one camshaft. The energy developed in the combustion chambers by combustion of a fuel within an oxidant is transmitted by each piston to a crankshaft.
For the management of the internal combustion engine, it is important to know the “phasing” (also called “synchronization”) of the engine. The term “phasing” refers to the precise determination of the stroke of the engine cycle (for an internal combustion engine of 4-stroke type they are: admission, compression, combustion, exhaust) which the engine is in for each of its cylinders. The precise position within a stroke of the engine cycle is usually established by determining the position of the crankshaft. However, for an internal combustion engine of 4-stroke type, the duration of an engine cycle in a combustion chamber corresponds to two complete revolutions of the crankshaft. Thus, to ascertain the phasing of an internal combustion engine of this type, an additional item of information is necessary. It is then customary to obtain this item of information on the basis of a camshaft position sensor. Indeed, a camshaft has a rotation speed corresponding to half the rotation speed of the corresponding crankshaft and, therefore, traverses only one revolution over the duration of a complete 4-stroke engine cycle.
Customarily, the position sensor corresponding to the crankshaft cooperates with a target comprising a large number of teeth (generally thirty-six or sixty, without taking account of one or two missing teeth making it possible to define an origin on the target) while the target used in cooperation with the camshaft sensor exhibits only few teeth (for example four). The signal provided by the sensor corresponding to the crankshaft is then used to precisely ascertain the position of the crankshaft (and therefore of the pistons).
However, when the signal of this sensor is defective or noisy, provision is made to use the signal emanating from the sensor corresponding to a camshaft in degraded mode.
The signals provided by the sensors corresponding to the crankshaft and to at least one camshaft are injected into an electronic device, such as for example a generic timer module GTM. Within this module, a digital phase locked loop DPLL is provided for managing the synchronization of the engine position and generating an angular clock.
While the engine is stopping, the crankshaft oscillates about an equilibrium position corresponding to the engine stopping position. If it is desired to then rapidly start the engine after it has stopped, it is important to precisely ascertain the engine stopping position. Novel position sensors, also called bidirectional sensors, are making it possible, on the one hand, like the sensors of the prior art, to detect an edge corresponding to a tooth but also, on the other hand, to determine the direction of rotation of the corresponding target. A strategy integrated into the digital phase locked loop makes it possible to take account of the item of information relating to the direction of rotation of the target and thus to ascertain the position of the engine when the latter stops.
A bidirectional sensor of known type, for example from document JP 2005 233622, provides signals exhibiting an active level and an inactive level. The duration of active level depends on the direction of rotation of the target. For example, a double duration of active level can be chosen for a reverse rotation with respect to the duration of active level for a rotation in the usual direction. It is thus possible to determine for each new edge the corresponding direction of transit. A corresponding strategy in the digital phase locked loop is then used for the realization of the angular clock.
However, there exist bidirectional sensors operating according to another principle. The direction of rotation of the target is given in the signal by varying for example the voltage corresponding to the active level and/or to the inactive level. Such a sensor is also known from document JP 2005 233622, FIG. 6, whose signal comprises four different levels.